We have described a distinct set of neutralizing antibodies obtained from patients who effectively control HIV-1. These antibodies have several properties. (1) Unlike most neutralizing antibodies, they more effectively neutralize CCR5-using (R5) isolates than CXCR4-using (X4) isolates. (2) They incorporate sulfate into their antigen binding site tyrosines, thereby mimicking CCR5, which uses the same modification to bind gp120. (3) They derive overwhelmingly from only one of 53 possible heavy-chain variable region genes. Due to a duplication event, individuals express from zero to four alleles of this variable chain gene (VH1-69). This class of antibodies is likely to be important because (1) their epitope on gp120 is conserved; (2) R5, not X4, isolates are transmitted to new hosts; and (3) viruses that expose their CCR5-binding site appear to be selected for during transmission. The specific aims of this proposal are to (1) establish the presence and diversity of tyrosine-sulfated antibodies in HIV-1 infected and uninfected individuals, and correlate the number of such antibodies in infected individuals with coreceptor-binding-site recognition and the breadth of neutralization of their sera; (2) correlate the amount of VH1-69-derived antibody with CCR5-binding-site recognition and with variation at the VH1-69 locus; (3) assay the ability of chimeric molecules that include a sulfated peptide derived from the CDR3 of one such antibody to neutralize virus, and identify additional sulfated peptides that may be useful in this context. These studies will describe the role of this class of antibodies in the control of HIV-1, and lay the groundwork for more comprehensive proteomic studies of the antibody response to HIV-1.